Anionic polymerization of methyl methacrylate initiated with molybdenum and tungsten chloride/organolithium/triisobutylaluminum systems

Molybdenum chloride (MoCl₅ or 1a ) and tungsten chloride (WCl₆ or 1b )/phenyllithium (PhLi)/triisobutylaluminum (iBu₃Al) systems were found to be quite effective for controlling the anionic polymerization of methyl methacrylate (MMA), affording high molecular weight poly(methyl methacrylate)s (PMMAs; number‐average molecular weight > 100,000) with narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight < 1.25) quantitatively at 0 °C for 1 h in toluene. Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) analyses of PMMAs obtained with the 1a and 1b /organolithium (RM; n‐butyllithium, PhLi)/iBu₃Al systems revealed that the initiation of MMA with the systems occurred by a nucleophilic attack of H^? to the monomer. In addition, the MALDI‐TOF MS analyses indicated that the presence of iBu₃Al was responsible for the controlled polymerization by improving the uniformity of the polymerization with respect to initiation and termination and by preventing a backbiting reaction. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4302–4315, 2002     

Anionic polymerization of methacrylate monomers initiated by lithium dialkylamides

The anionic polymerization of methacrylate monomers has been investigated with lithium dialkylamides as initiators in THF and toluene, respectively. Theoretical arguments and previous studies of mixed aggregates of lithiated organic compounds support the complexity of these systems. Lithium diisopropylamide (LDA) shows the highest initiation efficiency (e.g., f = 75% in THF at −78°C). Interestingly enough, lithium chloride has a remarkable beneficial effect on the methacrylates polymerization in THF at −78°C, due to the formation of 1 : 1 mixed dimer with LDA, which promotes a well-controlled anionic polymerization (M_w/M_n = 1.05) with a high initiation efficiency (94%). The less bulky lithium–diethylamide (LDEA) is much less efficient (f = 26%), essentially as a result of some associated “dormant” species and side reactions on the carbonyl group of MMA. Although various types of ligands have been screened, no remarkable improvement of LDEA efficiency has been observed. Lithium bis(trimethylsilyl)amide (LTMSA) has also been used to increase the steric hindrance of the initiator. This compound is, however, unable to initiate the methacrylates polymerization, more likely because of a too low basicity and a too strong Li—N bond. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3637–3644, 1997     

Anionic polymerization of methyl methacrylate initiated with late transition‐metal halides/organolithium/triisobutylaluminum systems

Anionic polymerization of methyl methacrylate (MMA) initiated with late transition‐metal halides [manganese chloride (MnCl₂), iron dichloride (FeCl₂), iron trichloride (FeCl₃), cobalt chloride (CoCl₂), or nickel bromide (NiBr₂)]/organolithium [nButyllithium (nBuLi) or phenyllithium (PhLi)]/triisobutylaluminum (iBu₃Al) systems is described. Except for the system with NiBr₂, the polymerizations of MMA afforded narrow molecular weight distribution poly(methyl methacrylate)s (PMMAs) with high molecular weights in quantitative yields at 0 °C in toluene. Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) analyses of the PMMAs obtained by the systems with FeCl₂, FeCl₃, and CoCl₂ revealed that the polymers had hydrogen (H) at both chain ends. Accordingly, the reaction of the transition‐metal halides with the organolithium in the presence of iBu₃Al should result in the formation of transition‐metal hydride [M‐H]^? species, which was nucleophilic enough to initiate the MMA polymerization. Because the presence of a six‐membered cyclic structure resulting from backbiting was confirmed from the MALDI‐TOF MS analyses of the PMMA obtained with the metal halide (FeCl₂, FeCl₃, or CoCl₂)/organolithium systems in the absence of iBu₃Al, the introduction of H at the ω‐chain end indicated that iBu₃Al should prevent the backbiting. However, the MnCl₂/nBuLi/iBu₃Al initiating system gave PMMAs bearing H at the α chain end and six‐membered cyclic structure at the ω chain end. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1962–1977, 2003     

Anionic polymerization of methyl methacrylate by initiating systems based on lithium amides of various secondary amines

The anionic polymerization of methyl methacrylate in toluene at −78 °C with lithium amides of various secondary amines (diisopropylamine, N‐isopropylaniline, N‐n‐butylaniline, indoline, and N‐ethyl‐o‐toluidine) as initiators was studied. The tacticity of the resulting poly(methyl methacrylate)s (PMMAs) was dependent on the kind of secondary amine, and highly isotactic PMMAs (91–93% mm) were obtained when lithium amides of N‐isopropylaniline and N‐n‐butylaniline were employed. The isotacticity of the PMMAs further increased up to 98% mm with initiating systems composed of the lithium amides, n‐butyllithium, and transition‐metal halides (WCl₆, MoCl₅, and NbCl₅). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4405–4411, 2005     

Anionic polymerization of methyl methacrylate initiated with lithium diphenylamide (Ph2NLi) in the presence of divalent transition metal halide

Anionic polymerization of methyl methacrylate (MMA) in the presence of divalent transition metal halide (MX₂ = FeBr₂, MnCl₂, CoCl₂, NiBr₂) was investigated. Initiating systems with various combinations of MX₂, lithium diphenylamide (Ph₂NLi), and organolithium (RLi, where R = nBu, Me) were effective to giving a high yield of poly(methyl methacrylate)s (PMMAs) at ?78 °C in toluene. The tacticity of the resulting PMMAs was highly dependent on the combination of the reagents used for the generation of the initiating systems within a syndiotactic (rr = 59%) to isotactic (mm = 65%) range. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 31–37, 2004     

Anionic graft copolymerization of methyl methacrylate with lithium diisopropylamide-treated poly(methyl α-substituted acrylate)s

The anionic grafting of methyl methacrylate onto several lithium diisopropylamide (LDA) — treated polymers of methyl α-substituted acrylates containing an active methylene or methine group was investigated. The grafting was carried out using a mole ratio of LDA/acrylate unit of 0.75 in the feed polymer. The anionic graft copolymerizability of these acrylate polymers largely depends upon the surrounding of the active α-hydrogen atom adjoining a carbonyl group or of the carbanion produced by the LDA treatment in the feed polymer.     

Ultrasonically initiated emulsion polymerization of methyl methacrylate

The ultrasonically initiated emulsion polymerization of methyl methacrylate (MMA) was investigated. Experimental results show that sodium dodecyl sulfonate (SDS) surfactant plays a very important role in obtaining a high polymer yield, because in the absence of SDS, monomer conversion is near zero. Thus, the surfactant serves as an initiator and as interfacial modifier in this system (MMA/H₂O), and the monomer conversion increases significantly with increasing SDS concentration. An increase in the reactor temperature also leads to an increase in the monomer conversion. An appropriate increase in the N₂ purging rate also leads to higher conversion. The conversion of MMA decreases with increasing monomer concentration because of the higher viscosity of the system. With the experimental results, optimized reaction conditions were obtained. Accordingly, a high monomer conversion of about 67% and a high molecular weight of several millions can be obtained in a period of about 30 min. Furthermore, transmission electron micrographs show that the latex particles prepared are nanosized, indicating a promising technique for preparing nanoscale latex particles with a small amount of surfactant. In conclusion, a promising technique for ultrasonically initiated emulsion polymerization has been successfully performed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3356–3364, 2001     

Photoinitiated polymerization of methyl methacrylate and methyl acrylate with 14C-labeled benzoin methyl ethers

Three ¹⁴C-labeled benzoin methyl ether (α-methoxy-α-phenylacetophenone) derivatives were utilized as photoinitiators in the polymerization of methyl methacrylate (MMA) and methyl acrylate (MA). The results of polymer end-group analysis are in accord with a mechanism of benzoin ether photocleavage into initiator radicals and dispute earlier labeling studies which were interpreted as evidence for copolymerization of excited-state benzoin ethers with reactive monomers. In MMA polymerization, the results indicate a preference for termination by disproportionation (～60%) and provide evidence for primary radical termination at 0.041M photoinitiator (optically dense solutions) in neat MMA. Evidence for chain branching by initiator radical hydrogen abstraction from poly(methyl acrylate) (PMA) is also presented. The benzoyl and α-methoxybenzyl radicals, produced on photolysis of benzoin methyl ether, appear to be equally effective in both initiation and hydrogen-abstraction processes. Quantum yields at 366 and 313 nm indicate the absence of a wavelength effect.     

High polymerization of methyl methacrylate with organonickel/MMAO systems

A series of nickel complexes, including Ni(acac)₂, (C₅H₅)Ni(η³‐allyl), and [NiMe₄Li₂(THF)₂]₂, that were activated with modified methylaluminoxane (MMAO) exhibited high catalytic activity for the polymerization of methyl methacrylate (MMA) but showed no catalytic activity for the polymerization of ethylene and 1‐olefins. The resulting polymers exhibited rather broad molecular weight distributions and low syndiotacticities. In contrast to these initiators, the metallocene complexes (C₅H₅)₂Ni, (C₅Me₅)₂Ni, (Ind)₂Ni, and (Me₃SiC₅H₄)₂Ni provided narrower molecular weight distributions at 60 °C when these initiator were activated with MMAO. Half‐metallocene complexes such as (C₅H₅)NiCl(PPh₃), (C₅Me₅)NiCl(PPh₃), and (Ind)NiCl(PPh₃) produced poly(methyl methacrylate) (PMMA) with much narrower molecular weight distributions when the polymerization was carried out at 0 °C. Ni[1,3‐(CF₃)₂‐acac]₂ generated PMMA with high syndiotacticity. The NiR(acac)(PPh₃) complexes (R = Me or Et) revealed high selectivity in the polymerization of isoprene that produced 1,2‐/3,4‐polymer at 0 °C exclusively, whereas the polymerization at 60 °C resulted in the formation of cis‐1,4‐rich polymers. The polymerization of ethylene with Ni(1,3‐tBu₂‐acac)₂ and Ni[1,3‐(CF₃)₂‐acac]₂ generated oligo‐ethylene with moderate catalytic activity, whereas the reaction of ethylene with Ni(acac)₂/MMAO produced high molecular weight polyethylene. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4764–4775, 2000     

Anionic polymerization of Lewis acid-activated methyl methacrylate by enamines

A novel ionic polymerization of methyl methacrylate (MMA) with a series of enamines (1) in the presence of methylaluminum bis(2,6-di-tert-butylphenoxide) (2) was examined. Both nucleophile (1) and electrophile (2) are indispensable for the present polymerization, in which (1) acts as initiator and (2) as activator. MMA polymerization proceeded smoothly in toluene at or below room temperature (r.t.) in the presence of 1 and 2 (1 ∼ 4 mol %, respectively), went to completion within 1 h, and afforded syndiotactic-rich PMMA with molecular weight distribution (M_w/M_n) in the 1.1 ∼ 1.4 range. The number-average molecular weight (M_n) of the polymer was significantly higher than that calculated from the feed ratio of 1 to the monomer, indicating low initiating efficiency. Kinetic studies coupled with isolation of an intermediate species proved that the real monomeric species involved in both initiation and propagation was a complex of MMA with 2. The effects of the concentrations of 1, 2, and MMA as well as the temperature of polymerization were also examined. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3671–3679, 1999     

Anionic graft polymerization of methyl methacrylate on starch and dextrin

The anionic graft polymerization of methyl methacrylate on the potassium alkoxide derivative of starch or dextrin in DMSO was studied. The effects of monomer and alkoxide concentrations as well as temperature were investigated. The yield of graft polymer increased with increasing alkoxide concentration. With increasing monomer concentration and with increasing temperature the extent of homopolymer formation increased. The composition of the graft polymers was found to depend on the reaction conditions. Graft polymers having about 10–40% poly(methyl methacrylate) were obtained. There were quantitative differences in yield of isolated graft polymer between starch and dextrin and these were ascribed to differences in the solubility properties of the carbohydrates. Evidence on the structure of the graft polymers and on the mechanism of the graft polymerization was obtained from acid hydrolysis of the graft polymers and determination of the molecular weights of the cleaved side chains.     

Anionic graft polymerization of methyl acrylate to protein functional groups

Graft polymerization of methyl acrylate to functional groups in proteins was studied with model compounds and with whole gluten proteins. Polymerization was carried out in the presence of sodium hydride or sodium in dimethyl sulfoxide. Initiation proceeds by an anionic mechanism, and the rate-determining step is the production of the initially formed carbanion. The rate of disappearance of methyl acrylate was followed via gas chromatography. Amino acid analyses indicated that the functional groups of the amino acids, as well as the peptide bonds, were acting as the initiation sites in proteins. Reaction rates of the functional groups were determined on model compounds in the presence of sodium and sodium hydride. With both the model compounds and the proteins, polymerization was initially rapid and then leveled off, although rates depended on the concentration of activator and acrylate. Methoxyl group analyses of modified model compounds and proteins indicated that from 5 to 10 methyl acrylate residues were introduced per reactive site.     

γ-radiation-initiated emulsion polymerization of n-butyl acrylate and of methyl methacrylate

We have investigated the γ-radiation-initiated polymerization of n-butyl acrylate (BA) and of methyl methacrylate (MMA) in aqueous emulsions stabilized with sodium lauryl sulfate (SLS). The reaction rate, as measured by a nonabsolute thermocouple technique, varies as the square root of emulsifier concentration for both monomers. In the case of BA, the dose rate exponent of the reaction rate is 0.7 ± 0.3, whereas the corresponding value for MMA is approximately 0.4. The overall activation energy of the BA polymerization is close to zero, whereas for MMA a value of 4.8 ± 2.1 kcal/mole has been found. The poly(butyl acrylate) molecular weight is effectively independent of soap concentration and of dose rate but decreases as the reaction temperature is increased in the range 30–70°C. The general conclusion drawn from this work is that these radiation-induced emulsion polymerizations differ little from conventionally initiated systems insofar as the reaction kinetics are concerned. Poly(butyl acrylate-g-methyl methacrylate) copolymers have been prepared by a direct irradiation method involving a poly(butyl acrylate) prepolymer seed latex. Some physical properties of this material have been examined.     

Kinetics of polymerization of methyl methacrylate initiated with cyclohexanone. Part I

The kinetics of radical polymerization of methyl methacrylate were investigated in a dioxane solution with cyclohexanone as initiator. It was found that the overall rate of reaction initiated with cyclohexanone (R_p) is proportional to the concentration of monomer and to the square root of the concentration of the initiator. The effect of temperature on the R_p in the temperature range of 65–95°C was discussed. The Arrhenius activation energy E_a estimated for the temperature range of 65–75°C was 137 kJ mol^?1.     

Vinyl polymerization. 364. Polymerization of methyl methacrylate initiated with benzaldehyde

Benzaldehyde (PhCHO) is found to be able to initiate the radical polymerization of methyl methacrylate (MMA). The rate of polymerization is expressed by the following equation: R_p = const[PhCHO]^0.5[MMA]^1.5. The overall activation energy is estimated to be 56.3 kJ mole^?1. The mechanism of polymerization is discussed.